Transistorized ignition system



J. R- LEFTWICH TRANSISTORIZED IGNITION SYSTEM Filed Oct. 24, 1965 BALLAST BIAS RESISTOR BIAS RESISTOR BREAKER RESISTOR OVER- SEMICONDUCTOR VOLTAGE IGNITION SWITCH MEANS PROTECTION COI L MEANS BATTERY POINTS SPARK G DISTRIBUTOR lNVENTOR JAMES R LEFTWICI-I ATTORN United States Patent 3,347,218 TRANSISTORIZED IGNITION SYSTEM James R. Lettwich, Indianapolis, Ind, assignor to P. R. Mallory & Co. inc, Indianapolis, Ind., a corporation of Delaware Filed Oct. 24, I965, Ser. No. 504,409 7 Claims. (Cl. 123-148) ABSTRACT OF THE DISCLOSURE A transistorized ignition system having a low value impedance device that shunts transient high voltages around a transistor switch means during the collapse of the magnetic field of a cooperatively associated inductance means.

The present invention relates to a firing system for internal combustion engines, and has particular relevance to means and methods for protecting semiconducting devices used therein from high surge voltages brought about by a collapse of a magnetic field of an inductance means.

The conventional ignition used by most automobile manufacturers on mass produced automobiles is a relatively simple but workable device. Generally, breaker points are utilized to interrupt an electrical current through an inductive means such as an ignition coil. To be eifective, the opening of the breaker points must by synchronized with the movement of the associated pistons of the internal combustion engine. In order for the conventional system to be effective for its intended purpose, the compression of the gas must be at a predetermined value and the piston must be at a predetermined position within its cooperatively associated cylinder. This should correspond to the instant of time when the breaker point opens causing a collapse of the magnetic energy of the ignition coil thereby inducing a relatively high voltage in the coil. The high voltage present in the coil is applied across a spark gap means, such as a spark plug, causing a spark to appear across the spark gap means. The spark causes the compressed mixture of fuel and air to ignite and explode. The expanding gases initiate another cycle for the piston. The conventional system has faults some of which are that the breaker points are subjected to excessive wear due to the fact the points are called up to periodically interrupt high currents flowing into an inductive load. In addition, the conventional system has poor starting characteristics as the induced voltage of the secondary Winding is interrupted by the breaker points which is slowest when the internal combustion engine is being turned over by the starting motor.

Several types of semiconduction ignition systems are known. Generally, the presently known semiconductor ignition system utilizes a semiconductor, such as a transistor, which controls the current flowing in the primary winding of the ignition coil. The transistorized ignition system greatly reduces the wear of the breaker points since the breaker points are only used to bias the transistor to conduction or non-conduction, and secondly, the semiconductor system provides a current that biases the semiconductor switches on and off rapidly regardless of the turnover speed of the internal combustion engine as initiated by the starter motor.

However, the aforementioned transistorized ignition system and in particular, the semiconductor is subjected to transient or high energy voltage pulses which may cause permanent damage to the semiconductor. Unsatisfactory attempts have been made to protect the semiconductor from transient voltages by using high impedance 3,347,218 Patented Get. 17, 1196? ICC devices to protect the transistor. However, in certain instances it has been found that the high impedance device cannot dissipate the energy of the transient voltage rapidly enough to protect the transistor from permanent damage.

The present invention makes use of a low impedance means to shunt the high transient voltages around the transistor thereby preventing these transient voltages from being applied across the transistor. It was also found that the selection of the resistive values of the low impedance device not only allows the selection of the discharge rate of the energy stored in the ignition coil, but in addition, allows the selection of the voltage value at which the discharge rate is initiated.

Therefore, it is an object of the present invention to provide a semiconductor ignition system having a low value impedance device that shunts the transient high voltages around the transistor switch means.

Another object of the present invention is to provide a semiconductor ignition system having a low value impedance device that allows the selection of the discharge rate of energy stored in the ignition coil of the system.

Yet another object of the present invention is to provide a semiconductor ignition system cooperatively associated with an internal combustion engine which allows more eflicient operation of the internal combustion engine than theretofore thought possible.

A further object of the present invention is to provide a semiconductor ignition system which is relatively simple and economical in construction, yet efiicient in operation.

Still another object of the present invention is to provide a semiconductor ignition system which will operate a multicylinder internal combustion engine.

Another object of the present invention is to provide a semiconductor ignition system which produces sparks of substantially constant value across a spark gap means.

Yet another object of the present invention is to provide a semiconductor ignition which is simple, etlicient, and effective.

Still another object of the present invention is to provide a semiconductor ignition system wherein due to primary winding of the ignition coil discharging through a low impedance device in a forward direction, very high energy coils may be used.

A further object of the present invention is to provide a semiconductor ignition system that has a fast response.

The present invention, in another of its aspects, re lates to the novel features of the instrumentalities of the invention described herein for teaching the principal object of the invention and to the novel principles em ployed in the instrumentalities whether or not these features and principles may be used in the said object and/or in the said field.

With the aforementioned objects enumerated, other objects will be apparent to those persons possessing ordinary skill in the art. Other objects will appear in the following description, appended claims, and appended drawings. The invention resides in the novel construction, combination, arrangement, and cooperation of ele- .ments as hereinafter described and more particularly as of an ignition system utilizing semiconductor means in accordance with the present invention.

Generally speaking, the present invention relates to a means and method for periodically interrupting an electrical current flowing through an ignition coil. A source of current is coupled to the primary and the secondary winding of an inductance means. The inductance means is used for storing a magnetic field. A switch means is coupled to the inductance means. A means for periodically providing a path for bias current to the switch is utilized. The bias current is used for biasing the switch to a conducting mode so as to provide a path for the current flow from the source of current through the inductance to the switch to ground. The flow of current produces a magnetic field in the inductance means. A spark gap means is coupled to the inductance means so that a collapse of the magnetic field caused by a cessation of current flow from the current source produces a spark across the spark gap means. An overvoltage protection means is coupled across the primary winding of the inductance means. The overvoltage protection means provides a low impedance shunt path bypassing the switch when the collapsing magnetic field exceeds a predetermined magnitude.

More particularly, the present invention pertains to an ignition system for an internal combustion engine. A source of direct current is connected to the primary and the secondary winding of an inductance means. The inductance means is utilized for storing a magnetic field. A transistor switch means has its emitter coupled to the inductance means and its collector coupled to ground. A diode is coupled between the emitter and the collector of the transistor. The diode is utilized for limiting the voltage stress on the transistor. A breaker point means is utilized for periodically providing a path for the bias current from the source of direct current to the base of the transistor. The bias current is used for biasing the transistor switch to conduction so as to provide a path for current flow from the source of direct current through the inductance means to the emitter of the transistor. The current flow produces a magnetic field in the inductance means. A spark gap means is coupled to the inductance means so that a collapse of the magnetic field caused by the cessation of current flow from the direct current source due to the opening of the breaker points produces a spark across the spark gap means. An overvoltage protection means including a silicon controlled rectifier and a zener diode, coupled between the gate and the anode of the silicon controlled rectifier, is coupled across the primary winding of the inductance means. The silicon controlled rectifier provides a low impedance shunt path bypassing the transistor switch when the collapsing magnetic field exceeds a predetermined magnitude. The silicon controlled rectifier is commutated by the oscillation of the inductance means.

Referring now to the drawing, which illustrates an embodiment of the present invention, the ignition system is indicated by the numeral 10. A source of direct current such as battery means 11 has its negative terminal coupled to ground and its positive terminal coupled to one side of an inductance means such as ignition coil 12.

The ignition coil includes a primary winding 13 and a secondary winding 14. The point at which the positive side of the battery is coupled to the ignition coil is also the common coupling means between the primary winding and the secondary winding of the ignition coil. The other side of the primary winding of the ignition coil is coupled in series with a ballast resistor 15. The ignition coil and the ballast resistor are designed to have such values as to provide maximum ignition performance and yet maintain the semiconductor stresses within a predetermined region.

The ballast resistor has its other end coupled to an overvoltage protection means 16. A silicon controlled rectifier 17 has its anode coupled in series with the ballast resistor 15. The cathode of the silicon controlled rectifier is coupled through a resistor 18 to the positive side of the battery means 11. The gate of the controlled rectifier is coupled to the anode of a zener diode 19 through a series connected resistor 20. The cathode of the zener diode is coupled to the anode of the silicon controlled rectifier.

The aforementioned overvoltage protection means in its utilization of the zener diode and the silicon controlled rectifier makes efficient use of the high speed switching characteristic and the high current carrying capability of these semiconductive devices. The semiconductor devices do not breakdown until a predetermined voltage level is exceeded at which time the silicon controlled rectifier provides a low impedance shunt path for the high voltage of the coil. When the high voltage in the overvoltage protection means reverses polarity, the silicon controlled rectifier is force commutated by the reverse flow of energy from the primary winding of the coil to the cathode of the controlled rectifier.

A semiconductor switch means 21 is coupled to one side of the ballast resistor 15 as illustrated in FIGURE 2. The semi-conductor switch means includes a PNP transistor 22. The emitter of the transistor is coupled to the ballast resistor and the collector of the transistor is coupled to ground. Coupled between the emitter and the collector of the transistor is a diode 23. As shown in FIGURE 2, the diode has its cathode coupled to the collector of the transistor. The base of the transistor is coupled to ground through a bias resistor 24 and breaker point means 25. A capacitor 26 is coupled between the base and the collector of the transistor. A second bias resistor 27 is coupled between the base and the emitter of the transistor.

It is noted that the ignition coil is connected in series with the emitter of the transistor through the ballast resistor. The diode is connected between the emitter and the collector of the transistor so as to prevent deleterious voltage stress from appearing across the transistor which would damage the transistor. The diode clamps the voltage rise across the transistor to a safe value.

As shown in the figures of the drawing, the output of the secondary winding is coupled in series to ground through a distributor means 28 and a spark gap means 29. The distributor means has a movable contact (not shown) which is adapted for engaging one of a plurality of fixed contacts (not shown). The movable contact is mechanically driven by the internal combustion engine. Also driven by the internal combustion engine in proper sequence with the operation of the distributor is a cam (not shown) for actuating the breaker point means 25. The fixed contacts are each connected to a spark gap means 29 such as a spark plug. While only a single spark gap means is illustrated, it is understood that the present invention is not limited thereto, but there may be a plurality thereof.

With the hereinbefore structural disclosure in mind and by continued reference to the several figures of the drawing, the following analysis of the operation of the present invention will further serve to amplify the novelty of the present invention.

Upon closing of the breaker point means 25, it is seen that the base and the collector are coupled to ground thereby substantially shorting out the resistance of the transistor. A flow of current takes place from the battery through the primary winding coil, through the ballast resistor to ground by way of the collector of the transistor. The flow of current through the primary win-ding of the ignition coil causes a magnetic field to exist in the ignition cor Upon opening of the breaker point switch 25, the transistor is biased to non-conduction so as to prevent the additional flow of current from the battery through the transistor. The cessation of current fiow through the ignition coil causes a collapse of the magnetic field of the coil.

The coil voltage reverses polarity and increases very rapidly in magnitude due to the transformer action of the coil. The resultant increase in magnitude of the coil voltage causes a spark to appear across the spark gap means to thereby ignite a mixture of fuel and air.

As the reverse voltage in the primary winding attains the breakdown voltage of the zener diode 19 plus the gating voltage of the silicon controlled rectifier 17, the zener diode and the controlled rectifier are biased to conduction. The high magnitude of reverse voltage flows in the following path of from the primary winding of the ignition coil, through the ballast resistor, through the silicon controlled rectifier, through the resistor 18 back to the primary winding. The resistive components of the aforementioned loop dissipate almost all of the surge voltage during the first oscillation. As the surge goes negative, the silicon controlled rectifier is biased to nonconduction. The ignition coil thereafter oscillates to remove the residual stored energy.

While the invention is illustrated and described in an embodiment, it will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of this invention and as set forth in the appended claims.

Having thus described my invention, I claim:

1. An ignition system for an internal combustion en gine comprising: a source of direct current; an inductance means having a primary and a secondary winding coupled to said source of direct current, said inductance means for storing a magnetic field; a semiconductor switch means coupled to said inductance means; breaker point means for periodically providing a path for bias current from said source of direct current to said semiconductor switch, said bias current biasing said semiconductor switch to conduction so as to provide a path for current flow from said source of direct current through said inductance means to said semiconductor switch, said current flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current source by opening of said breaker point means produces a spark across said spark gap means; and an overvoltage protection means including a silicon controlled rectifier coupled across said primary winding of said inductance means, said silicon controlled rectifier providing a low impedance shunt path bypassing said semiconductor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon cont-rolled rectifier commutated by oscillation of said inductance means.

2. An ignition system for an internal combustion engine comprising: a source of direct cur-rent; an inductance means having a primary and a secondary winding coupled to said source of direct current, said inductance means for storing a magnetic field; a semiconductor switch means coupled to said inductance means; breaker point means for periodically providing a path for bias current from said source of direct current to said semiconductor switch, said bias current biasing said semiconductor switch to conduction so as to provide a path for current flow from said source of direct current through said inductance means to said semiconductor switch, said current flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current source by opening of said breaker point means produces a spark across said spark gap means; and an overvoltage protection means including a silicon control-led rectifier and a zener diode, said zener diode coupled between the gate and the anode of said silicon controlled rectifier, said overvoltage protection means coupled across said primary winding of said inductance means, said silicon controlled rectifier providing a low impedance shunt path bypassing said semiconductor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon controlled rectifier commutated by oscillation of said inductance means.

3. An ignition system for an internal combustion engine comprising: a source of direct current; an inductance means having a primary and a secondary winding coupled to said source of direct current, said inductance means for storing a magnetic field; a transistor switch means having its emitter coupled to said inductance means and to its base through bias resistor means and its collector coupled to ground; breaker point means for periodically providing a path fior bias current from said source of direct current to the base of said transistor switch, said bias current biasing said transistor switch to conduction so as to provide a path for current flow from said source of direct current through said inductance means to said emitter of said transistor switch, said current flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current source by the opening of said breaker point means produces a spark across said spark gap means; and an overvoltage protection means including a silicon controlled rectifier and a zener diode, said zener diode coupled between the gate and the anode of said silicon controlled rectifier, said overvoltage protection means coupled across said primary winding of said inductance means, said silicon controlled rectifier providing a low impedance shunt path bypassing said transistor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon controlled rectifier commutated by oscillation of said inductance means.

4. An ignition system for an internal combustion engine comprising: a source of direct current; an inductance means having a primary and a secondary Winding coupled to said source of direct current, said inductance means for storing a magnetic field; a transistor switch means having its emitter coupled to said inductance means and its collector coupled to ground; breaker point means for periodically providing a path for bias current from said source of direct current to the base of said transistor switch, said bias current biasing said transistor switch to conduction so as to provide a path for current flow from said source of direct current through said inductance means to said emitter of said transistor switch, said current flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current by the opening of said breaker point means produces a spark across said spark gap means; and an overvoltage protection means including a silicon controlled rectifier and a zener diode, said zener diode coupled between the gate and the anode of said silicon controlled rectifier, said overvoltage protection means coupled across said primary winding of said inductance means, said silicon controlled rectifier providing a low impedance shunt path bypassing said transistor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon controlled rectifier commutated by oscillation of said inductance means.

5. An ignition system for an internal combustion engine comprising: a source of direct current; an inductance means having a primary and a secondary winding coupled to said source of direct current, said inductance means for storing a magnetic field; a transistor switch means having its emitter coupled to said inductance means and its collector coupled to ground; a diode coupled between said emitter and said collector of said transistor, said diode limiting the voltage stress on said transistor; breaker point means for periodically providing a path for bias current from said source of direct current to the base of said transistor switch, said bias current biasing said transistor switch to conduction so as to provide a path for current flow from said source of direct current through said inductance means to said emitter of said transistor switch, said cur-rent flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current by the opening of said breaker point means produces a spark across said spark gap means; and an overvoltage protection means including a silicon cont-rolled rectifier and a zener diode, said zener diode coupled between the gate and the anode of said silicon controlled rectifier, coupled across said primary winding of said inductance means, said silicon controlled rectifier providing a low impedance shunt path bypassing said transistor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon controlled rectifier commutated by oscillation of said inductance means.

'6. An ignition system for an internal combustion engine comprising: a source of direct current; an inductance means having connected primary secondary windings coupled to said source of direct current, said inductance means for storing a magnetic field, a transistor switch means having its emitter coupled to said inductance means and to the base of said transistor means through a bias means and its collector coupled to ground; a diOde coup-led between said emitter and said collector of said transistor, said diode limiting the voltage stress on said transistor; breaker point means for periodically providing a path of bias current from said source of direct current to said base of said transistor switch, said bias current biasing said transistor switch to conduction so as to provide a path fior current flow from said source of direct current through said inductance means to said emitter of said transistor switch, said current flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current source by the opening of said breaker point means produces a spark across said spark gap means; and an over-voltage protection means coupled across said primary winding of said inductance means including a silicon controlled rectifier and a zener diode, said zener diode coupled between the gate and the anode of said silicon controlled rectifier, said silicon controlled rectifier providing a low impedance shunt path bypassing said transistor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon controlled rectifier commutated by oscillation of said inductance means.

7. An ignition system for an internal combustion engine comprising: a source of direct current; an inductance means having connected primary and secondary windings coupled to the positive side of said source of direct current, said inductance means for storing a magnetic field; a transistor switch means having its emitter coupled to said inductance means and to the base of said transistor means through bias means and its collector coupled to ground; a diode coupled between said emitter and said collector of said transistor, said diode limiting the voltage stress on said transistor; breaker point means for periodically providing a path for bias current from said source of direct current to the base of said transistor switch, said bias current biasing said transistor switch to conduction So as to provide a path for current flow from said source of direct current through said inductance means to said emitter of said transistor switch, said current flow producing a magnetic field in said inductance means; a spark gap means coupled to said inductance means such that a collapse of said magnetic field caused by cessation of current flow from said direct current source by opening of said breaker point means produces a spark across said spark gap means; and an over-voltage protection means coupled across said primary winding of said inductance means including a silicon controlled rectifier and a zener diode, the cathode of said zener diode coupled to the gate and the anode of said zener diode coupled to the cathode of said silicon controlled rectifier, said silicon controlled rectifier providing a low impedance shunt path bypassing said transistor switch when said collapsing magnetic field exceeds a predetermined magnitude, said silicon controlled rectifier commutated by oscillation of said inductance means.

References Cited UNITED STATES PATENTS 2,925,548 2/1960 Schever 31716' 3,016,477 1/1962 Naborowski 123148 X 3,222,575 12/1965 Dexter 317-20 3,264,521 8/1966 Huntzinger et al. 123-148 X OTHER REFERENCES Silicon Controlled Rectifier. General Electric Company.

Page 51 of December 1958, TK 2798 G 4 c. 3.

LAURENCE M. GOODRIDGE, Primary Examiner. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING: A SOURCE OF DIRECT CURRENT; AN INDUCTANCE MEANS HAVING A PRIMARY AND A SECONDARY WINDING COUPLED TO SAID SOURCE OF DIRECT CURRENT, SAID INDUCTANCE MEANS FOR STORING A MAGNETIC FIELD; A SEMICONDUCTOR SWITCH MEANS COUPLED TO SAID INDUCTANCE MEANS; BREAKER POINT MEANS FOR PERIODICALLY PROVIDING A PATH FOR BIAS CURRENT FROM SAID SOURCE OF DIRECT CURRENT TO SAID SEMICONDUCTOR SWITCH, SAID BIAS CURRENT BIASING SAID SEMICONDUCTOR SWITCH TO CONDUCTION SO AS TO PROVIDE A PATH FOR CURRENT FLOW FROM SAID SOURCE OF DIRECT CURRENT THROUGH SAID INDUCTANCE MEANS TO SAID SEMICONDUCTOR SWITCH, AND CURRENT FLOW PRODUCING A MAGNETIC FIELD IN SAID INDUCTANCE MEANS; A SPARK GAP MEANS COUPLED TO SAID INDUCTANCE MEANS SUCH THAT A COLLAPSE OF SAID MAGNETIC FIELD CAUSED BY CESSATION OF CURRENT FLOW FROM SAID DIRECT CURRENT SOURCE BY OPENING OF SAID BREAKER POINT MEANS PRODUCES A SPARK ACROSS SAID SPARK GAP MEANS; AND AN OVERVOLTAGE PROTECTION MEANS INCLUDING A SILICON CONTROLLED RECTIFIER COUPLED ACROSS SAID PRIMARY WINDING OF SAID INDUCTANCE MEANS, SAID SILICON CONTROLLED RECTIFIER PROVIDING A LOW IMPEDANCE SHUNT PATH BYPASSING SAID SEMICONDUCTOR SWITCH WHEN SAID COLLAPSING MAGNETIC FIELD EXCEEDS A PREDETERMINED MAGNITUDE, SAID SILICON CONTROLLED RECTIFIER COMMUTATED BY OSCILLATION OF SAID INDUCTANCE MEANS. 